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When a slice of potato is dropped into hot oil, it gets fried but the same in hot water, gets ‘cooked’. What is it about oil that gives the slice of potato the crispy feature while water only makes it soft?

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    $\begingroup$ Semi-relevant: youtube.com/watch?v=a4gYv2BK-HQ $\endgroup$ – Curt F. Nov 28 '17 at 8:35
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    $\begingroup$ Thanks for the link @CurtF. It is interesting to know about fluorinert. But I really do not see the point. In fact, it has me a little more intrigued. The chip out of F.C.-40 was as crispy as the one out of canola oil. But then the former had a lot less fat. I understand why it has less fat but then, how did the slice get fried at all, does it all come down to dehydration? Because even a microwave oven fries things by removing water by getting it to excite.. $\endgroup$ – Swaroop Chandra Nov 28 '17 at 13:32
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    $\begingroup$ Related: Why does water boil vegetables, but oil does not? $\endgroup$ – Mithoron Nov 28 '17 at 15:57
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    $\begingroup$ What temperature is a fryer? What temperature is boiling water? $\endgroup$ – Jon Custer Nov 28 '17 at 17:04
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Oil can get hotter than the b.p. of water, 373 K.

The browning (decomposition) of starches proceeds very slowly (perhaps years for a noticeable change) at 373 K. In addition, the water in the potato will not evaporate away, since the potato is in water (not the water vapor above the liquid, which can be hotter than 373 K). Since the cooking oil is hotter (e.g. 440 K), starch decomposes (caramelizes) in a few minutes, and dehydration makes the chip crunchy. Bon appétit!

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